1. Field of the Invention
The present invention relates to dispersion compositions which are particularly useful as coatings, whether used alone or in combination with other coating materials. The dispersions are comprised of acrylate and/or methacrylate based addition polymer in an organic liquid, and are stabilized using a specialized kind of stabilizer developed to enable the dispersion compositions of the present invention.
2. Description of the Background Art
Dispersions of addition copolymers in organic liquids are described in EP-A-0172589, published Feb. 26, 1986 and entitled: Dispersion of Addition Copolymers in an Organic Liquid, which is hereby incorporated by reference. These dispersions are useful in providing a coating having a glossy finish for wood, plastic materials and metal, and have been used to provide a coating having a metallic appearance. However, many of the coatings having a metallic appearance are used as exterior finishes for automobiles and other equipment exposed to weathering and acid rain. Typically these exterior finishes are provided using a weather-resistant basecoat/clearcoat coating system wherein the basecoat having a metallic appearance is protected by an overlaying clearcoat. The dispersions described in EP-A-0172589 are not suitable for use in basecoat/clearcoat coating systems of the type which provide a high gloss metallic appearance.
The basecoat/clearcoat systems require the application of two coatings. The first coating applied is a basecoat which comprises a basic polymer which provides a coating film as well as additives and adjuvants, pigments, colorants and dispersing agents. The second coating applied provides a clear coating film over the surface of the basecoat, to obtain a high gloss. Upon application of the clearcoat, the orientation of pigment particles in the underlaying basecoat can be affected in a manner detrimental to the metallic appearance of the basecoat, rendering such basecoats unsuitable for use in the system.
The ability of the basecoat to provide and retain orientation of the pigment particles required for the metallic appearance is increased when higher solids basecoat formulations can be used (for example about 40% by weight solids or greater). Higher solids basecoats depend on the stabilizer used to maintain the dispersion of the basecoat solids in the organic liquid from which the solids are applied to the surface to be coated.
Aqueous dispersions of acrylic polymers stabilized using a particular copolymer to obtain high solid coatings are disclosed in EP-A-0238108, published Sept. 23, 1987, and entitled: Aqueous Dispersion Of An Addition Polymer, A Coating Composition Based Thereon And A Process For Coating A Substrate With Such Coating Composition, which is hereby incorporated by reference. Such aqueous dispersion stabilizers, while similar, are not suitable for use in organic liquid based dispersions.